222,687 research outputs found
Cryogenic loss monitors with FPGA TDC signal processing
Radiation hard helium gas ionization chambers capable of operating in vacuum
at temperatures ranging from 5K to 350K have been designed, fabricated and
tested and will be used inside the cryostats at Fermilab's Superconducting
Radiofrequency beam test facility. The chamber vessels are made of stainless
steel and all materials used including seals are known to be radiation hard and
suitable for operation at 5K. The chambers are designed to measure radiation up
to 30 kRad/hr with sensitivity of approximately 1.9 pA/(Rad/hr). The signal
current is measured with a recycling integrator current-to-frequency converter
to achieve a required measurement capability for low current and a wide dynamic
range. A novel scheme of using an FPGA-based time-to-digital converter (TDC) to
measure time intervals between pulses output from the recycling integrator is
employed to ensure a fast beam loss response along with a current measurement
resolution better than 10-bit. This paper will describe the results obtained
and highlight the processing techniques used.Comment: 7 pp. 2nd International Conference on Technology and Instrumentation
in Particle Physics 2011: TIPP 2011. 9-14 Jun 2011. Chicago, Illinoi
Edge States and Broken Symmetry Phases of Laterally Confined He Films
Broken symmetries in topological condensed matter systems have implications
for the spectrum of Fermionic excitations confined on surfaces or topological
defects. The Fermionic spectrum of confined (quasi-2D) He-A consists of
branches of chiral edge states. The negative energy states are related to the
ground-state angular momentum, , for Cooper pairs. The
power law suppression of the angular momentum, for , in the fully gapped 2D
chiral A-phase reflects the thermal excitation of the chiral edge Fermions. We
discuss the effects of wave function overlap, and hybridization between edge
states confined near opposing surfaces on the edge currents, ground-state
angular momentum and ground-state order parameter. Under strong lateral
confinement, the chiral A phase undergoes a sequence of phase transitions,
first to a pair density wave (PDW) phase with broken translational symmetry at
. The PDW phase is described by a periodic array of
chiral domains with alternating chirality, separated by domain walls. The
period of PDW phase diverges as the confinement length .
The PDW phase breaks time-reversal symmetry, translation invariance, but is
invariant under the combination of time-reversal and translation by a one-half
period of the PDW. The mass current distribution of the PDW phase reflects this
combined symmetry, and orignates from the spectra of edge Fermions and the
chiral branches bound to the domain walls. Under sufficiently strong
confinement a second-order transition occurs to the non-chiral "polar phase" at
, in which a single p-wave orbital state of Cooper pairs
is aligned along the channel.Comment: 16 pages, 16 figure
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An empirical investigation of the relationship between the real economy and stock returns for the United States
This paper tests for the relationship between excess returns and economic growth rates in the U.S., using a
Seemingly Unrelated Regression (SUR) approach. The system includes monthly data for inflation, consumption,
narrow money supply and personal disposable income and each equation has up to 24-lagged Autoregressive
terms. After removing the four major shocks associated with Black Monday, the Asian Crisis, “9·11” and its
anniversary, we cannot find any ARCH behaviour in either the excess returns or the money series. The models
are reduced to their parsimonious forms and the inflation and real consumption equations are corrected for
ARCH. To make the result more robust we reduce our system to four equations by conditioning on income and
testing the remaining equations for stability. The SUR model suggests strong long-run feedback between the
financial sector and the real economy firstly through inflation, then consumption while the influence of real
money supply appears transitory. Consumption is more sensitive to the economic variables in short and long run
as compared with stock market windfalls
Strong Phases in the Decays B to pi pi
Two sources of strong phases in the decays to are identified:
(1) "quasi-elastic scattering" corresponding to intermediate states like
and , (2) ``'' corresponding to intermediate
states like and . Possibilities of using data to
identify these two sources are discussed and illustrated. Present data suggests
both sources may be significant.Comment: 6 pages, 1 figure
X-ray Polarization Signatures of Compton Scattering in Magnetic Cataclysmic Variables
Compton scattering within the accretion column of magnetic cataclysmic
variables (mCVs) can induce a net polarization in the X-ray emission. We
investigate this process using Monte Carlo simulations and find that
significant polarization can arise as a result of the stratified flow structure
in the shock-ionized column. We find that the degree of linear polarization can
reach levels up to ~8% for systems with high accretion rates and low
white-dwarf masses, when viewed at large inclination angles with respect to the
accretion column axis. These levels are substantially higher than previously
predicted estimates using an accretion column model with uniform density and
temperature. We also find that for systems with a relatively low-mass white
dwarf accreting at a high accretion rate, the polarization properties may be
insensitive to the magnetic field, since most of the scattering occurs at the
base of the accretion column where the density structure is determined mainly
by bremsstrahlung cooling instead of cyclotron cooling.Comment: 7 pages, 8 figures, accepted by MNRA
Direct and secondary nuclear excitation with x-ray free-electron lasers
The direct and secondary nuclear excitation produced by an x-ray free
electron laser when interacting with a solid-state nuclear target is
investigated theoretically. When driven at the resonance energy, the x-ray free
electron laser can produce direct photoexcitation. However, the dominant
process in that interaction is the photoelectric effect producing a cold and
very dense plasma in which also secondary processes such as nuclear excitation
by electron capture may occur. We develop a realistic theoretical model to
quantify the temporal dynamics of the plasma and the magnitude of the secondary
excitation therein. Numerical results show that depending on the nuclear
transition energy and the temperature and charge states reached in the plasma,
secondary nuclear excitation by electron capture may dominate the direct
photoexcitation by several orders of magnitude, as it is the case for the 4.8
keV transition from the isomeric state of Mo, or it can be negligible,
as it is the case for the 14.4 keV M\"ossbauer transition in
. These findings are most relevant for future nuclear quantum
optics experiments at x-ray free electron laser facilities.Comment: 17 pages, 7 figures; minor corrections made; accepted by Physics of
Plasma
One-spin quantum logic gates from exchange interactions and a global magnetic field
It has been widely assumed that one-qubit gates in spin-based quantum
computers suffer from severe technical difficulties. We show that one-qubit
gates can in fact be generated using only modest and presently feasible
technological requirements. Our solution uses only global magnetic fields and
controllable Heisenberg exchange interactions, thus circumventing the need for
single-spin addressing.Comment: 4 pages, incl. 1 figure. This significantly modified version accepted
for publication in Phys. Rev. Let
Authorization and access control of application data in Workflow systems
Workflow Management Systems (WfMSs) are used to support the modeling and coordinated execution of business processes within an organization or across organizational boundaries. Although some research efforts have addressed requirements for authorization and access control for workflow systems, little attention has been paid to the requirements as they apply to application data accessed or managed by WfMSs. In this paper, we discuss key access control requirements for application data in workflow applications using examples from the healthcare domain, introduce a classification of application data used in workflow systems by analyzing their sources, and then propose a comprehensive data authorization and access control mechanism for WfMSs. This involves four aspects: role, task, process instance-based user group, and data content. For implementation, a predicate-based access control method is used. We believe that the proposed model is applicable to workflow applications and WfMSs with diverse access control requirements
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